The present invention relates to radiation curable compositions. More particularly, the present invention relates to compositions containing vinyl ether functional siloxanes and an aromatic iodonium salt or aromatic sulfonium salt photoinitiator which are curable upon exposure to actinic radiation.
Radiation curable compositions which contain alkenyl ether functional organosilicon compounds have been described in the art. For example, U.S. Pat. No. 4,617,238 to Crivello discloses and claims a photopolymerizable composition comprising (a) an organopolysiloxane having at least one Si-bonded vinyloxy functional group of the formula H.sub.2 C.dbd.CH--O--G--, where G is alkylene (such as propylene) or alkylene interrupted by at least one divalent heteroradical selected from --O--, divalent phenylene, or substituted divalent phenylene, or combination of such heteroradicals, and (b) an onium salt catalyst. The '238 patent also describes a method wherein the vinyl ether group is introduced into the organopolysiloxane by addition (hydrosilylation) of compounds with an allyl and a vinyl ether group to an SiH group of the organopolysiloxane in the presence of a platinum catalyst. In the method of the '238 patent, only the allyl group is added to the SiH group while the vinyl ether group is preserved and thus only one vinyl ether group for each SiH group can be incorporated into the siloxane molecule at any given time.
European Patent Publication No. 0462389 teaches thermosetting organopolysiloxanes with oxyalkylene vinyl ether groups bonded by SiOC groups and the vinyl groups may be substituted by alkyl radicals. EPO'389 also teaches a method for the preparation of these compounds and their application as photochemically thermosetting polysiloxanes in encapsulating compounds, as non-stick coating compounds for flat carriers or as modified additives in compounds which can be thermoset radically, cationically or by UV or electron radiation.
German Patent Publication No. DE 4142327 discloses iodonium salts which are suitable as photoinitiators for polymerizing cationically polymerizable organic substances such as epoxides, vinyl ethers, epoxy group containing organopolysiloxanes, and alkenyloxy group (such as vinyloxy or propenyloxy groups) containing organopolysiloxanes.
Brown et al., in U.S. Pat. No. 5,270,423 discloses organosilicon compounds with a siloxane portion of the general formula --OR'OCH.dbd.CHR" linked via an SiOC bond wherein R' is a divalent hydrocarbon radical and R" is hydrogen or an alkyl radical which are useful in radiation curable compositions, in which they are mixed with an initiator. The compositions are particularly useful in UV radiation curable coatings.
However, none of the references cited hereinabove disclose the particular diaryliodonium salt catalysts of this invention in combination with the unique vinyl ether functional polysiloxanes of the instant invention.